1. Field of the Invention
The present invention relates to a processing unit to be incorporated into an electrophotographic apparatus such as a laser printer. More particularly, the invention relates to a developing unit to be incorporated into an electrophotographic apparatus.
2. Description of the Related Art
The conventional laser printer has a processing cartridge comprising a photoconductive member, a processing means including a charger, a developing unit and a cleaning unit, and a case containing the photoconductive member and the processing means. The processing cartridge is detachably mounted on the main frame of the laser printer. When the consumable component such as the photoconductive member needs to be replaced or the processing cartridge needs to be replenished with toner, the case containing the photoconductive member and the processing means is removed from the main frame of the laser printer. This processing cartridge is replaced with a new processing cartridge when the toner contained in the developing unit thereof is exhausted.
Replacing the used processing cartridge with a new processing cartridge instead of individually replacing the used consumable components of the used processing cartridge with new ones facilitates the replacement of the used consumable components and prevents making the operator's hands dirty, damaging the new consumable components and deteriorating picture quality. On the other hand, since the used processing cartridge is replaced with a new one when the toner of the used processing cartridge is exhausted, the photoconductive member and the charger of the used processing cartridge, which have a comparatively long service life and therefore are still serviceable, are discarded. This unnecessary waste increases the running cost of the laser printer and is not desirable from the view point of resources conservation and environmental protection.
A laser printer provided with a developing unit formed separately from other processing means and capable of operating at a comparatively low running cost has been proposed. In this laser printer, the developing unit is replenished with toner, and other processing means are not replaced when the toner contained in the developing unit is exhausted. This previously proposed laser printer provided with the developing unit that can be replenished with toner is described with reference to FIGS. 6A and 6B. The developing unit of the laser printer shown in FIGS. 6A and 6B is of a pseudo two-component toner system using a mixed developer prepared by mixing magnetic toner and magnetic carrier.
Referring to FIGS. 6A and 6B, a processing unit 80 consists of a developing unit 82 comprising a developing device 82A and a toner hopper 82B, and a processing subunit 84 comprising a photoconductive member 84A, a charger 84B and a cleaning device 84C. The developing unit 82 and the processing subunit 84 are contained in a case 86, and the case 86 is detachably mounted on the main frame 88 of a laser printer. The developing unit 82 and the processing subunit 84 can be individually removed from the case 86.
In case the laser printer is jammed, the case 86 containing the developing unit 82 and the processing subunit 84 is removed from the main frame 88 as shown in FIG. 6A. When the toner is exhausted, only the developing unit 82 is taken out from the case 86 without removing the case 86 from the main frame 88, and the empty toner hopper 82B is replaced with a new toner hopper containing toner to replenish the developing unit 82 with toner. When the photoconductive member needs to be replaced, the processing subunit 84 is taken out from the case 86 without removing the case 86 from the main frame 88, and then the used processing subunit 84 is replaced with a new one.
When the developing unit 82 is in an initial state, the developing unit 82 may be provided with a primary toner hopper containing initial developer containing carrier, and a secondary toner hopper containing replenishment toner. Either the primary toner hopper or the secondary toner hopper may be used as occasion demands. The developing device 82A may be charged with initial developer beforehand, or the developing device 82A may be provided with a sealed chamber filled with initial developer and the sealed chamber containing the initial developer may be unsealed when starting to use the developing unit 82 to supply the initial developer to the developing sleeve 90 of the developing device 82A.
The developing unit provided with both the primary toner hopper and the secondary toner hopper needs two toner hoppers respectively for containing the initial developer and the replenishment toner, which increases the manufacturing cost of the developing unit. Furthermore, there is the possibility that the operator may accidently use the primary toner hopper and the secondary toner hopper mistakenly.
The developing unit provided with the developing device charged beforehand with initial developer has the disadvantage that there is the possibility that the initial developer may spill from the developing device during the transportation of the developing unit. Thus, the developing device must be sealed with a special seal to prevent the initial developer from spilling from the developing device. Further, the operator's hands may be soiled when removing the seal.
Additionally, the developing unit provided with the developing device having the sealed chamber containing the initial developer has the disadvantage that there is the possibility that developer adhering to the seal removed from the developing device will soil the surroundings and the operator's hands.